Trend changes in sympatric Subantarctic and Antarctic fur seal pup populations at Marion Island, Southern Ocean
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Date
Authors
Wege, Mia
Etienne, Marie-Pierre
Oosthuizen, Wessel Christiaan
Reisinger, Ryan Rudolf
Bester, Marthan Nieuwoudt
De Bruyn, P.J. Nico
Journal Title
Journal ISSN
Volume Title
Publisher
Wiley
Abstract
Recent pup population estimates of sympatric Subantarctic (Arctocephalus tropicalis)
and Antarctic fur seals (A. gazella) at Marion Island are presented. Published
pup population estimates of A. tropicalis (1995 and 2004) with an unpublished total
island count in 2013, and annual counts on subsets of rookeries (2007–2015) were
analyzed using a hierarchical Bayesian model. The pup population declined by 46%
(95% credible interval CI: 43%–48%) between 2004 (mean = 15,260, CI: 14,447–
16,169 pups) and 2013 (mean = 8,312, CI: 7,983–8,697), mirrored by a 58%–60%
decline at rookeries counted annually (2007–2015). Population decline was highest
at high-density west and north coast rookeries, despite negligible change in female
attendance patterns, pup mortality or median pupping date over the previous 25 yr.
A better understanding of foraging behavior and its effects on reproductive success
and survival in this A. tropicalis population is needed before we can attribute population
decline to any external factors. In contrast, total island counts of A. gazella pups
in 2007, 2010, and 2013, suggest that this population is still increasing although
the annual intrinsic rate of population growth decreased from 17.0% (1995–2004,
744 pups) to 4.0% (2010–2013, 1,553 pups). The slowed growth of A. gazella is
likely the result of saturation at the main rookery
Description
Keywords
Arctocephalus, Subantarctic fur seal, Antarctic fur seal, Population estimate, Marion Island, Hierarchical Bayesian model, Detection probability, Sympatry, Density, Count
Sustainable Development Goals
Citation
Wege, M, Etienne, MP, Oosthuizen, WC, Reisinger, RR, Bester, MN & De Bruyn, PJN 2016, 'Trend changes in sympatric Subantarctic and Antarctic fur seal pup populations at Marion Island, Southern Ocean', Marine Mammal Science, vol. 32, no. 3, pp. 960-982.